Transposition of the great vessels is a serious form of congenital heart disease (see congenital heart defects, in which the two major vessels that carry blood away from the heart (the aorta and the pulmonary artery) are transposed. This means that insufficient oxygenated blood is supplied to the body's tissues.

Cyanosis (blueness of the skin) usually develops and the baby becomes increasingly short of breath and feeds poorly. Open heart surgery may be needed in order to correct the defect.